Why does eating excess carbs/proteins cause you to gain fat?

i have an essay exam for A.P. Bio but i am kind of stuck. i know it has to do with the amount and that the stomach stores extra glucose produced as fat, but why else considering protein isn’t broken down to glucose?

carbs are broken down into sugars which are used as energy, the more you eat the more potential energy you have. When you do not use this energy up it is stored as fat. If you eat less carbs, more potential energy can be used by burning fat

Hypoglycemia / Hypoglycaemia